Technical Abstract:
The use of vaccination to control bovine viral diarrhea virus (BVDV) infections presents exceptional challenges due to the nature of the virus, the unique interaction of the virus with the immune system, and its ability to establish persistent infections. The lack of proof reading function during the replication of the BVDV single-stranded genome, results in variability between the genomes of different generations of virus. This variability leads to any one strain of the virus existing as a viral swarm rather than a single entity. This in turn leads to genetic drift which over time has given rise to division of BVDV into two different species and numerous subgenotypes. The BVDV genome may also undergo recombination which gives rise to differences in biotype, cytopathic and noncytopathic, and perhaps differences in virulence. Cytopathic and noncytopathic viruses interact differently with the immune system. One outcome of these differences is that noncytopathic viruses may establish persistent infections, whereas cytopathic viruses do not. Because persistently infected (PI) animals shed virus throughout their life span, presence of PI animals in the population ensures that BVDV remains in circulation. The constant circulation of BVDV due to PI animals hampers control efforts.